Ultrasound in pregnancy
A prenatal ultrasound (also known as echography or sonogram) is a non-invasive test, which uses sound waves to create an image of the baby, the placenta and the uterus, and also other organs situated in the mother’s womb.
The obstetrical ultrasound was used for the first time at the end of the 1950s and has now become a very useful diagnosis tool in Obstetrics.
As highlighted by Doctor Roberto Rodríguez, in his monograph: “Introducción a las ecografías en el embarazo”, this imaging technique is useful because, depending on the period of the pregnancy, it can have a decisive impact. The image provided makes it possible:
- To choose the best time at which to extract the foetus, i.e. when there is sufficient maturity, thereby preventing any damagethat occurs when the pregnancy is maintained under some special circumstances (intrauterine growth retardation, uropathies, gastroschisis).
- The treatment needed by the new-born infant can be planned and referred to the most suitable hospital along with the necessary medical equipment prepared for any intervention.
- There are complications which require an essential emergency intervention at the time of the birth. If they are known in advance, suitable measures will be taken.
- Some alterations can be resolved according to the guidance of the ultrasound by treating the foetus inside the uterus. Examples of these situations include intrauterine transfusion in cases of Rh incompatibility, laser coagulation of placental vessel communications in twin pregnancies with twin-to-twin transfusion syndrome (very serious situation, with a high risk that the twins will die if this action is not taken), pleural effusion drainage, the placement of a balloon in the trachea in cases of diaphragmatic hernia, etc.
- There are many significant abnormalities, many of which are incompatible with life outside the uterus. In these cases, depending on the legislation in each country, one available option is the termination of the pregnancy.
In these final cases, the arrival of the Nace Test has made one of the greatest contributions to non-invasive prenatal diagnosis in recent times. Due to its reliability, and with a mother’s blood sample, it can be determined within 72 hours whether the foetus is affected by Down’s syndrome, Edwards’ Syndrome or Patau’s Syndrome. The safety and efficacy of the test is 99.7% for Down’s Syndrome. In actual fact, many specialists are already recommending it as an alternative to the amniocentesis.
In the past 40 years there have been many studies on the safety and reliability of ultrasound in pregnancy but, despite the advances in technology, the margin of error of the test in establishing, for example, the gestational age stands at 8%, as featured in a report of the journal Journal of Midwifery & Women’s Health .
The same report points out the limitations of ultrasounds in the following terms: “their accuracy depends largely on the ability of the technician performing the test and the quality of the images, not to mention the size of the patient or the foetal position.”
The American College of Obstetricians and Gynaecologists (ACOG) only recommends a prenatal ultrasound between weeks 18 to 20.
In Spain, the pregnant woman normally undergoes 3 of these scans:
- The first takes place in weeks 11–13 and is used to determine the situation of the placenta, the number of foetuses and the nuchal fold (combined test of the first trimester).
- The second in weeks 18–20 to examine the formation of organs and possible development irregularities.
- The third occurs in weeks 33–34 to assess foetal growth, detect placenta or amniotic fluid pathologies, or a late defect (although these are usually diagnosed in the previous ultrasound scan).